There is known a method of forming a preset film on a substrate by an atomic layer deposition method or a method of etching a film formed on the substrate by an atomic layer etching method (see, for example, Patent Documents 1 and 2). In these methods, the preset film is formed on the substrate or the film formed on the substrate is etched by supplying different kinds of gases to the substrate within a processing vessel in sequence.
Further, there is also known an etching method (an etching method using continuous plasma) in which a processing condition is switched from a gas condition of one etching process to a gas condition of another etching process while maintaining plasma, in order to shorten an etching time when etching an etching target film having several kinds of insulating films stacked on top of each other, for example (See, for example, Patent Document 3).
Patent Document 1: Japanese Patent Laid-open Publication No. H09-027396
Patent Document 2: Japanese Patent Laid-open Publication No. 2015-173240
Patent Document 3: Japanese Patent Publication No. 5,014,435
In the aforementioned methods, however, a part of a gas, which is once exhausted from a region where the substrate is provided within the processing vessel to a downstream side region thereof, may flow back into the region where the substrate is provided within the processing vessel. If such a backflow of the gas occurs, a time of replacing the gas is lengthened when changing the gas. Further, since a next process may be performed in a state that the gas is not sufficiently replaced, the process may be unstably performed.